This invention relates generally to electronic control of automotive engines and, more particularly, to a method and apparatus for inferring fuel mixture based on the processing of exhaust gas sensor data.
The combustion of air/fuel mixtures in internal combustion engines, such as those found in automobiles, produces an exhaust gas stream comprised of various gaseous components, such as hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). Those skilled in the art will appreciate that oxides of nitrogen refers to both NO and NO2.
Attempts to eliminate or control these components have involved the use of three-way catalysts (TWC). Such catalysts typically oxidize HC and CO, while simultaneously reducing NOx. However, optimizing both the oxidation of HC and CO and the simultaneous reduction of NOx requires close control of the air/fuel (A/F) ratio entering the internal combustion engine. Optimum reduction of all three components occurs when the A/F ratio is close to stoichiometric or xcex=1, i.e., 14.65 kilograms of air to 1 kilogram of gasoline for a commonly used fuel. It will be appreciated that xcex is the excess air/fuel factor and is defined by dividing the quantity of air and fuel actually supplied by the theoretical stoichiometric air/fuel requirement.
In order to achieve and maintain the desired A/F ratio, exhaust gas oxygen (EGO) sensors and closed-loop control circuits have been used in conjunction with three-way catalysts. Such emission control systems generally measure the oxygen concentration of the exhaust gas and adjust the relative amounts of air and fuel supplied to the engine in response thereto. EGO sensors provide a feedback adjustment whenever the air/fuel ratio is other than a predetermined level, i.e., xcex=1, to indicate whether the mixture is richer (xcex less than 1) or leaner (xcex greater than 1) than xcex=1. This level is known as the closed loop control point and, within narrow limits, may be selected as desired, i.e., other than xcex=1.
Electronic engine control systems operate in a variety of modes depending on engine conditions, such as starting, rapid acceleration, sudden deceleration, and idle. Under closed-loop control, the amount of fuel delivered is determined primarily by the concentration of oxygen in the exhaust gas, the concentration of oxygen in the exhaust gas being indicative of the ratio of air and fuel that has been ignited.
Engines which are capable of operating on different fuels, such as gasoline, methanol, or a. mixture of the two, utilize electronic engine control systems to change the engine operating parameters in response to the type of fuel being delivered to the engine. Such systems utilize a sensor to detect the type of fuel being delivered to the engine and an electronic engine controller to vary the operating parameters accordingly. An instance of such a system is disclosed in Curran et al. in U.S. Pat. No. 5,230,322. A drawback to such systems is the cost of the flexible fuel sensor. Furthermore, in the event that the flexible fuel sensor fails, the operating parameters which are dependent on the output of the fuel type sensor will be erroneous.
The present invention proposes a method of determining whether the fuel being used is gasoline or an alternative type of fuel such as ethanol and avoids the need for a fuel type sensor. The determination of fuel type, in accordance with the present invention, is based on analyzing the signal from the exhaust gas oxygen (EGO) sensor. As previously stated, an EGO sensor is normally provided in the fuel control system of the vehicle for monitoring the oxygen content of the exhaust gas in order to permit the air/fuel ratio to be changed as necessary to maintain a stoichiometric value. Thus, the cost of identifying the fuel type as proposed by the present invention, is substantially reduced. In accordance with the present invention, the determination of fuel type is based on the ratio of the value of certain characteristics of the signal during the rich and lean portions of the signal. One such characteristic is the area of the rich and lean portions of the signal waveform. Other characteristics such as signal length or period may also be used instead of or in combination with the area.